AuthorTopic: Earharts Radio Transmitter (Read 27638 times)

In a letter written on July 25, 1937 by Mr. Eric H. Chater, Manager of Guinea Airways, is the following paragraph

OUR WIRELESS OPERATOR REPORTS

THE CONDITION OF RADIO EQUIPMENT ON EARHART PLACE IS AS FOLLOWS - TRANSMITTER CARRIER WAVE ON 6210 KC'sWAS VERY ROUGH AND I ADVISED MISS EARHART TO PITCH HER VOICE HIGHER TO OVERCOME THE DISTORTION CAUSED BY THE ROUGH CARRIER WAVE, OTHERWISE THE TRANSMITTER SEEMED TO BE WORKING SATISFACTORILY.

From the above it appears that when Earhart arrived at Lae her radio transmitter was developing a problem. Mr. Chater detailed maintenance work that was done on the plane but he mentioned no work being done on the transmitter. So apparently the transmitter still had a rough carrier that distorted the voice modulation when Earhart took off for Howland Island. The Itasca radio operators had difficulty reading Earhart's transmission's. They attributed the distortion to the fact that her signals were so strong it caused their radio speakers to distort.

We can be certain that the very rough landing on the reef at Gardner Island didn't do Earhart's transmitter any good. I'm amazed that it even worked after the beating it probably took. All the transmissions heard after the landing appear to have been badly distorted. The operator on Nauru Island said it sounded like Earhart's voice but the signal was so badly distorted he couldn't understand a thing she said. The Pan Am operators heard numerous signals that were voice modulated by both male and female voices. They said the signals all had odd or wobbly modulation characteristics and they couldn't understand anything that was said.

The fact that Earhart's transmitter apparently was putting out a badly distorted signal helps sort out the post loss radio messages. Anyone who reported that they heard Amelia Earhart "loud and clear," in my opinion, wasn't listening to an Earhart transmission.

Interesting that Eric Chatter reported the carrier wave was rough, and to pitch her voice higher. This indicates there may have been a lower-frequency distortion or signal being added within the transmitter itself.

I don't know about symptoms, problems, or failure modes of a dynamotor high voltage supply as used in her Western Eelectric transmitter, but if the dynamotor had a bad winding, it might (an assumption) cause a varying high voltage, modulating the signal seperately of the voice modulation. Maybe someone familiar with dynamotors could comment.

I know Betty Klenck Brown reported the signal as faiding in and out, but did she recall a similar distortion in the voices?

I have some limited experience with dynamotor-powered WWII radios, but not with the specific kind used by Amelia. The most obvious characteristic of a dynamotor is the time lag to reach full output - taking a full 1 to 2 seconds to spin up. Amelia's radio was wired so the dynamotor was off until the microphone "talk" switch was pushed. (Before the Morse code key was removed, the system had the option of running the dynamotor constantly, providing a constant supply of power to the transmitter for code transmission.) This creates a characteristic rising whine heard at the start of each transmission, and tends to clip off anything said for the first half second or so. To make transmissions clear, the technique taught is to key the mike, then wait a moment before speaking.Dynamotors have commutator brushes, which can create a buzz or whine in the background if there isn't a filter, and especially if they're worn or dirty.The war-era Dynamotors I'm familiar with had no explicit voltage regulation circuit. They relied on the load to even things out, but even so the voltage could change quite a bit. This wasn't as big a problem for tube radios as one might expect - it meant a simpler circuit that worked well enough for general purposes.The supply voltage also effected the output voltage. If a dynamotor is running off of batteries, then the output voltage will decline as the battery supply voltage declines. I'm not enough of an expert to be able to predict what the effect might be on Amelia's radio.

The most obvious characteristic of a dynamotor is the time lag to reach full output - taking a full 1 to 2 seconds to spin up.

That is interesting in terms of Amelia possibly doing morse code with the mike button. The first dot or dash after a pause might end up missing with slowly transmitted code.

I looked at the basic schematics some time back, and I seem to recall that the transmitter also had key'ed filaments in the tubes (tube cathode heaters are off until the mike button is pushed). Years ago I had a WWII surplus BC654 that was like this. I wondered at the time how this might have affected her morse code, possibly clipping a leading dash into a dot.

The Itasca radio operators had difficulty reading Earhart's transmission's. They attributed the distortion to the fact that her signals were so strong it caused their radio speakers to distort.

I am a little unclear on this point. It does seem that the radio operators aboard Itasca had difficulty reading some of the transmissions from KHAQQ, but it appears mostly due to signals being too weak to copy. (I am thinking of those earlier signals when she was some ways out) Could you possibly site a reference to a time where it was reported that she was not understood by Itasca due to "distortion". That would be helpful.

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All the transmissions heard after the landing appear to have been badly distorted. The operator on Nauru Island said it sounded like Earhart's voice but the signal was so badly distorted he couldn't understand a thing she said.

Having read over the post signals analysis it is not clear to me that "all" the signals were distorted. Which particular ones are you referencing?When looking at the information we have on the reception from Radio Nauru it specifically states "voice not intelligible". It says nothing about distortion.Unintelligible speech could be due to a number of things, including poor modulation of the underlying carrier signal.

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The Pan Am operators heard numerous signals that were voice modulated by both male and female voices. They said the signals all had odd or wobbly modulation characteristics and they couldn't understand anything that was said.

I do recall reading a reception of some wobbly signals by Pan Am operators but not "all" of them. References here would be useful. I've been a ham operator for a long time and I am not clear about what "wobbly" means. Is a wobbly signal one that cannot be understood due to distortion? I'm not sure.

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The fact that Earhart's transmitter apparently was putting out a badly distorted signal helps sort out the post loss radio messages. Anyone who reported that they heard Amelia Earhart "loud and clear," in my opinion, wasn't listening to an Earhart transmission.

It's my understanding that there were at least a few times, prior to losing radio contact, when her transmissions were received "loud and clear" (or something very close to that) by Itasca, pointing to effective transmissions under some conditions. I support your work in attempting to find a way to separate the wheat from the chaff with these signals analysis, but I'm not quite sold on your final premise.

I am a little unclear on this point. It does seem that the radio operators aboard Itasca had difficulty reading some of the transmissions from KHAQQ, but it appears mostly due to signals being too weak to copy. (I am thinking of those earlier signals when she was some ways out) Could you possibly site a reference to a time where it was reported that she was not understood by Itasca due to "distortion". That would be helpful.

I am not going to get into this argument.

I have put together a transmission timeline that summarizes all of the transmissions received from AE during the fatal flight.

That data may or may not help resolve this particular dispute, but I do believe it is the data needed for an informed discussion.

All adventurers have back-up plans, just as Amelia did failing landfall at Howland she'd fly the pre-spcified 'north-south line'. Lamentably a plan not notified to sufficient, or sufficiently pertinent, people, or at least it was not coherently passed to those most involved. Today of course adventurers have 'Mission Control Centres'.

However there is much store attached to her radio communications good, bad, and indifferent, but non to an outright radio failure. It would seem reasonable to say had she known her radio had failed before reaching half-way to Howland she would have aborted and returned. But what if it failed nearer to Howland, would she and Itasca have intuitively expected and implemented 'plan B' - black smoke from Itasca, etc? All would now know the risk of missing Itasca would be great. More importantly, in failing to locate Howland wouldn't this have been when she justifiably and inherently expected all support personnel to know and respond to her survival plan to fly the 'north-south line' hopefully to an island. She may well have been under the loose expectation that a previously (but aborted) plan to construct an airstrip on Niku would probably be complete, or crash-landing usable? In ANY event wouldn't she, though frightened, have been blindly confident that search would follow her, WITHOUT fail? I purport she DID expect rescue from the north-south line even without radio communication, even for this survival recourse morse communication still did not enter her vital-requirement list. Basically if voice comms failed 'ground support' would prevail.

Tim, in a TIGHAR Tracks article "A landing on the Reef" there are three photos of the reef at Gardner Island. There weren't any big rocks on it but it still looks pretty rough to be used as a runway.

Bruce W Badgrow

Many thanks.

Video evidence touts the putative touchdown area as being ideal in both length and surface.

Richard Gifford, a retired airline captain who personally examined the putative landing site on Niku in 2001, told me in 2011 that that area is scattered with numerous potholes, but "otherwise smooth." A rough landing is certainly imaginable and Captain Gifford has speculated an airplane might sustain some damage. The speculated landing area is good enough, but hardly "ideal."

Richard Gifford, a retired airline captain who personally examined the putative landing site on Niku in 2001, told me in 2011 that that area is scattered with numerous potholes, but "otherwise smooth." A rough landing is certainly imaginable and Captain Gifford has speculated an airplane might sustain some damage. The speculated landing area is good enough, but hardly "ideal."

They're gooshy-soft by comparison to conventional tires and have a large foot print so tend to 'average out' rough spots even as their resiliency absorbs protrusions and their size helps the craft 'float' over dimples, small and even fairly large.

Those big tires would be called Tundra Tires now days. With empty tanks, the Lockheed would perform rather like an Alaska bush plane, which handle landing on river bars with rocks "as large as shoe boxes". Amelia was planning for unimproved runways, rather than off-airport landings I assume.

I am addressing the particular argument that landing conditions on the Nutiran shore (map) are ideal for landing an aircraft. I am respectfully advancing the modest idea in its stead that landing conditions there are less than perfect but still survivable, with some possible damage to aircraft and its occupants.

We can talk about the Electra's tires and their marvelous ability to absorb shock, but consider:

1) Again, the area is studded with large potholes.

2) The worm gear on that particular Electra was not designed for force loading from the sides, as is caused by impact with a large pothole. Photos of the tire at the Luke Field ground loop accident are instructive.

3) So far as I know the aircraft was not equipped with shoulder restraints.

The argument was advanced by Bruce that a landing on the Nutiran shore would have been rough. I wasn't there to see it (if indeed it happened at all), but I find that narrow piece of his speculation reasonable. The opposing idea that the conditions there were "ideal in both length and surface" and that a rough landing there is simply an unreasonable thought not to be entertained seems to me at odds with the facts as they have been communicated to me, by Captain Gifford, who, after all, was there, and by others.

They had to get the airplane down with all of the following intact for transmissions to be possible: starboard prop, only generator (also on the starboard side), and a working fuel system from the tanks to the starboard engine. There were doubtless a few other things the aircraft had to have working to do what it supposedly did, but beyond those minimum requirements, other damage to the aircraft must be admitted as readily possible as a direct result of the ground conditions.

Also to consider:

Captain Gifford is often quoted that he could land a 747 there but not take off again. That implies to me either possible damage to the aircraft from landing it or subpar conditions on the takeoff field, or both.

Betty Brown and others who credibly intercepted radio transmissions said Noonan had been injured, perhaps in the landing.

Betty also told me in our telephone conversation that she thought she heard Earhart say "one engine is up." She did not write this down in the diary but remembered it later. Take this as a recalled memory from one who heard it, only this and nothing more.

I find the narrow argument I am making, of a rough but survivable landing on Nutiran with a relatively intact airplane, to be reasonable, and supported by the observable facts, tires notwithstanding. I just don't see the conditions as ideal or as anything one would attempt unless one's only other option was ditching at sea.

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